1. Field of the Invention
This invention relates generally to a periodic pulse forming circuit, and in particular is directed to a circuit for separating periodic pulses from a series of pulses which includes noise pulses.
2. Description of the Prior Art
In a professional type video tape recorder or VTR, the reproduced video signal is usually supplied to a time base error corrector (TBC) to eliminate time base errors, such as jitter, from the reproduced video signal. In order to detect the time base errors, it is necessary to separate the horizontal sync signal from the reproduced video signal. However, noise signals are often contained in the reproduced video signal as shown in FIG. 1A of the accompanying drawings so that such noise signals are detected by the horizontal sync separator as false sync signals such as N as shown in FIG. 1B. It is apparent that the horizontal sync pulses H including the false sync signal N disturb the correction of time base errors by the TBC, because the time base error is not detected accurately due to the false sync pulse.
In order to avoid the above problem, a conventional TBC is provided with a gate signal generator, such as a monostable multivibrator, which generates a gate signal which occurs simultaneously with the next succeeding horizontal sync signal based upon the preceding horizontal sync signal, as shown in FIG. 1C. The series of horizontal sync pulses including the false sync pulses are gated by the gate signal whereby the false sync pulses are cancelled.
However, when fast-motion reproduction or slow-motion reproduction is performed by moving a tape at a speed different from that used in recording, the interval between successive horizontal sync signals separated from the reproduced video signal will change correspondingly. As a result, it is impossible to separate accurately the horizontal sync signals from the reproduced video signal when using the conventional TBC circuit.